The present invention generally relates to rollover sensors and, more particularly, to cost affordable vehicle rollover detection with reduced sensor hardware and enhanced rollover discrimination for sensing a rollover condition of a vehicle.
Automotive vehicles are increasingly equipped with safety-related devices that deploy in the event that the vehicle experiences a rollover so as to provide added protection to the occupants of the vehicle. For example, upon detecting a vehicle rollover condition, a pop-up roll bar can be deployed such that, when activated, the roll bar further extends vertically outward to increase the height of support provided by the roll bar during a rollover event. Other controllable features may include deployment of one or more air bags, such as frontal air bags, side mounted air bags, and roof rail air bags, or actuating a pretensioner to pretension a restraining device, such as a seat belt or safety harness, to prevent occupants of the vehicle from ejecting from the vehicle or colliding with the roof of the vehicle during a rollover event.
In the past, mechanical-based rollover sensors have been employed in automotive vehicles to measure the angular position of the vehicle from which a rollover condition can be determined. The mechanical sensors have included the use of a pendulum normally suspended vertically downward due to the Earth""s gravitational force. Many mechanical automotive sensing devices are employed simply to monitor the angular position of the vehicle relative to a horizontal level ground position. As a consequence, such mechanical automotive sensors have generally been susceptible to error when the vehicle travels around a corner or becomes airborne, in which case the Earth""s gravitational force, which the sensor relies upon, may be overcome by other forces.
More sophisticated rollover sensing approaches require the use of as many as six sensors including three accelerometers and three angular rate sensors, also referred to as gyros, and a microprocessor for processing the sensed signals. The three accelerometers generally provide lateral, longitudinal, and vertical acceleration measurements of the vehicle, while the three gyros measure angular pitch rate, roll rate, and yaw rate. However, such sophisticated rollover sensing approaches generally require a large number of sensors which add to the cost and complexity of the overall system. In addition, many known sophisticated sensing systems are generally susceptible to cumulative drift errors, and therefore occasionally must be reset.
In an attempt to minimize the number of sensors required, some conventional rollover sensing approaches have employed, at a minimum, both an angular roll rate sensor and lateral accelerometer. For those sensors designed to detect both rollover and pitchover events, an angular pitch rate sensor and a longitudinal accelerometer are typically added. While the angular rate sensor can be integrated to calculate a roll angle, in practice, angular rate sensors typically generate a non-zero, time-varying output, even in the absence of a roll rate. This bias may cause a significant error in the integration generated roll angle, and such bias must be compensated in order to provide an accurate sensed measurement. Accordingly, many conventional rollover sensing approaches typically require auxiliary sensors, in addition to the angular rate sensor, to compensate for zero-input biases inherent in many angular rate sensors.
Another rollover sensing approach is disclosed in related application Ser. No. 09/725,645 entitled xe2x80x9cVEHICLE ROLLOVER DETECTION APPARATUS AND METHOD,xe2x80x9d filed on Nov. 29, 2000, which is commonly assigned to the assignee of the present application. The aforementioned approach employs an angular rate sensor generating a sensed roll rate signal which is integrated to produce a roll angle. The roll angle and sensed roll rate signals are processed by a microprocessor-based controller to generate a rollover deployment signal. This approach also employs a bias removal device which removes bias. However, this approach may require a partial reset when the integration window is contracted, which places a large computational burden on the microprocessor. In addition, microprocessor constraints on random-access memory (RAM) limit the width of the integration window, placing an upper limit on the maximum duration of a rollover event that can be properly sensed. This generally can result in small errors in the roll angle which could have an effect on concatenated events such as two-stage cross slope rollovers. Additionally, it remains difficult to ascertain a forthcoming rollover event for certain very near-rollover events.
Accordingly, it is therefore desirable to provide for an accurate and cost affordable rollover detection apparatus and method that minimizes signal bias. It is further desirable to provide for a rollover detection apparatus and method that provides improved immunity to non-rollover conditions during near-rollover events so as to prevent false rollover deployments during these driving events.
In accordance with the teachings of the present invention, a vehicle rollover sensing apparatus and method are provided for detecting an anticipated overturn condition of a vehicle, and thus allowing for the timely deployment of safety-related devices. The rollover sensing apparatus includes an angular rate sensor for sensing attitude rate of change of a vehicle and producing an angular rate signal indicative thereof, and a vertical accelerometer for sensing vertical acceleration of the vehicle and producing a vertical acceleration signal indicative thereof. The rollover sensing apparatus also has a controller including an integrator for integrating the attitude rate signal and producing an attitude angle. The controller determines an inclination angle of the vehicle based on the vertical acceleration signal and adjusts the roll angle as a function of the determined inclination angle. The controller further includes deployment logic for comparing the adjusted attitude angle and angular rate signal to a threshold limit, and providing a vehicle overturn condition signal based on the comparison.
According to another aspect of the present invention, a rollover detection apparatus and method is provided for detecting an anticipated overturn condition for a vehicle and providing immunity to near-rollover events. The apparatus comprises an angular rate sensor for sensing attitude rate of change of a vehicle and producing an attitude rate signal indicative thereof, an integrator for integrating the sensed attitude rate of change signal and producing an attitude angle, and deployment logic. The deployment logic compares the attitude angle and sensed attitude rate signal with a variable threshold defining a region of deployment and a region of no deployment. The deployment logic further detects the presence of a driving event, such as a near-rollover event, which causes at least one of a large attitude rate and a large attitude angle, and adjusts the variable threshold based on detecting the driving event so as to prevent deployment of a vehicle overturn condition. The output provides a vehicle overturn condition signal based on the comparison.
Accordingly, the rollover sensing apparatus and method of the present invention advantageously provides enhanced rollover detection with a minimal number of sensors to detect an overturn (e.g., rollover) condition of a vehicle. It should be appreciated that the apparatus and method employs an angular rate sensor and vertical accelerometer, without requiring other auxiliary sensors, to achieve cost efficient and accurate rollover detection. It should further be appreciated that the apparatus and method provide enhanced immunity to false rollover events, such as those events that approach a near-rollover condition.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.